The invention relates to power transmission belts having an engineered surface and more particularly, to power transmission belts having an engineered surface comprising a region having a nonwoven material comprising acrylic fiber.
It is known in the art to make power transmission belts from elastomeric materials having an embedded tensile member. The belts may describe a multi-rib, toothed, v-belt, or flat profile. The belts run in pulleys having a matching profile.
It is known to cover belt surfaces, including the back, sides, profile, and/or the rib flanks with various textile materials or fibers to modify the wear resistance, frictional properties, crack resistance, stiffness, and/or strength characteristics of the surface and/or the underlying elastomeric region. Special fabric characteristics and/or processes may be required to mold a profile. For example, a fabric can be preformed into the profile shape before molding, a tedious process step. More commonly, to avoid the preforming step, a fabric-covered toothed belt made by the flow-through process on a toothed mold requires a fabric that is expandable, such as one with a very low modulus and high elongation in at least one direction. A fabric-covered notched or toothed v-belt or multi-v-ribbed belt made inverted on a flat mandrel by pressing with a profiled outer mold likewise requires a fabric with high elongation (typically 40 to 100%) and with a low modulus in order to stretch from the initial flat configuration to the final profiled configuration without tearing or restricting profile formation. Satisfactory woven and knit fabrics comprising a variety of fiber materials are known for such applications. Representative of the art is U.S. Pat. No. 5,645,504 to Westhoff, wherein it is suggested that aramid, cotton, rayon, and acrylic yarns would be useful in weft-knitted, stretch fabrics for belt covering or reinforcement in clutching applications, because these materials have high enough melting temperatures to withstand the frictional heat in such applications. The only representative example provided was a belt with a knit fabric of yarns of aramid-rayon blend. Knit and woven fabrics with high stretch suitable for belts are relatively expensive.
A flocking process is known for manufacturing belts with a highly controlled amount and orientation of fiber on a belt surface. Representative of the art is U.S. Pat. No. 6,561,937 to Wegele, wherein the fabric on the drive surface of the belt is covered with perpendicularly oriented short fiber flock by means of an adhesive. A long list of fiber materials ostensibly may be used for the flock, including acrylic fibers, but no rationale is offered to aid in selecting a fiber type, and no acrylic examples are provided. Flocking adds additional process steps to the belt manufacturing process and requires specialized equipment.
Nonwoven fabrics (often referred to as “nonwovens”) have been proposed for covering profiled belt surfaces. Representative of the art is U.S. Pat. No. 6,793,599 to Patterson et al., U.S. Pat. No. 6,824,485 to Edwards et al., and U.S. Pat. No. 6,609,990 to Kopang. Nonwoven fabrics can provide an open structure that is easily penetrated by elastomer during molding, or a more closed structure that leaves a high concentration of fiber at the surface, and a variety of fabric materials are available for achieving desired frictional., thermal, and mechanical characteristics in the belt. Nonwovens can be processed in conventional belt-making equipment and offer cost savings over knits and woven fabrics.
In practice, however, it has been found that prior art nonwoven fabrics based on cellulosic fibers and cellulosic/synthetic blends have one or more undesirable characteristics. First, cellulosic materials have relatively poor durability, especially under wet operating conditions. Second, prior nonwovens have very limited stretch or elongation. Typically, in a tensile test, nonwovens stretch only 2 to 10% and then yield or tear so that subsequent extension is highly localized in the region of the tear. Likewise, when nonwovens are subjected to stretching during molding, the randomly arranged fibers simply slide over one another and separate, including breaking any bonds between fibers formed by adhesive binders if used. Unlike woven or knit fabrics, the stretching of nonwovens is very difficult to control, and frequently holes or tears are created by the separating fibers. Holes and tearing leads to irregular belt surfaces, excess rubber strike-through, and/or patches of exposed elastomer, resulting in poor wear resistance, noise, and/or poor friction control. Third, it has previously been difficult to control the penetration of rubber into the nonwoven fabric to achieve a desired surface characteristic, particularly when coupled with the tearing problem. Even after extensive investigation into the manipulation of known fabric variables, such as porosity, permeability, thickness, and tensile strength, or process variables, such as using multiple layers of nonwovens, improvements in processing and performance are needed.
Having investigated a large number of synthetic, natural, and blended nonwoven fabric materials, none of which produced belts entirely free of the previously mentioned defects, the inventors finally discovered a solution in the invention disclosed herein. What is needed is a power transmission belt having a pulley-engaging region comprising a nonwoven surface material, on or commingled with the underlying elastomer of the belt body, wherein the nonwoven material comprises acrylic fibers optionally blended with up to about 75% non-acrylic fibers, such as cellulosic fibers. What is needed is a power transmission belt with a multi-ribbed profile and having a nonwoven pulley-engaging surface layer and a compressive layer, with the nonwoven layer comprising acrylic fibers or micro-fibers, optionally blended with up to about 75% non-acrylic fibers. The present invention meets these needs.